Inbuilt __gcd() function is not working on Xcode macOS. I have run the following code on Xcode (macOS Catalina) it shows an error "Use of undeclared identifier '__gcd' ".
#include <iostream>
#include <algorithm>
using namespace std;
int main()
{
cout << "gcd(6, 20) = " << __gcd(6, 20) << endl;
return 0;
}
please help me out
You can use the one from <numeric> if you compile with -std=c++17
#include <numeric>
int main()
{
std::cout << "gcd(6, 20) = " << std::gcd(6, 20) << std::endl;
return 0;
}
Thanks for asking,
Use the following function below header files, as gcd is not working in mac m1:
int __gcd(int a, int b) {
if (b == 0) {
return a;
}
return gcd(b, a % b);
}
Then you can use __gcd(a, b) function easily and efficiently.
std::gcd() is available in c++17
otherwise,
The GCD for two non negative integers is easily calculated:
int gcd(int a, int b){ int c = a % b; while(c != 0) { a = b; b = c; c = a % b; } return b;}
cf. https://www.gamedev.net/forums/topic/358629-built-in-c-command-for-gcd/3354131/
Some answers, here, contain Euclidean based code for calculating gcd. For example :
int gcd(int a, int b) { if(b == 0){return a;} return gcd(b, a % b); }
You will have to take care about the order of actual arguments you pass to this function. Code is based on assumtion that a>0, b>0 and a>=b.
Code can be modified to remove these assumptions.
int gcd(int a,int b)
{
if(a<0 or b<0)
return -1;
if(a>b)
return gcd(b,a);
if(a==0)
return b;
//Due to Euclidean algorithm
return gcd(a,b%a);
}
If you stick to first version, you will have to take care about sending arguments according to the above assumptions.
